Metal organic frameworks for removal of compounds from a fluid

ABSTRACT

Embodiments provide a method of compound removal from a fluid. The method includes contacting one or more metal organic framework (MOF) compositions with a fluid and sorbing one or more compounds, such as CO 2 , H 2 S and condensable hydrocarbons. One or more of CO 2 , H 2 S and condensable hydrocarbons can be sorbed simultaneously or in series. The metal organic framework can be an M-soc-MOF.

BACKGROUND

As society continues to deplete fossil fuel reserves, alternate energysolutions are constantly sought after to supplant fossil fuel sources,such as biogas and natural gas with cleaner and more abundant energysources. Although natural gas is a fossil fuel, it is acknowledged as anexcellent alternative before a transition to cleaner energy solutions.However, natural gas often contains significant amounts of CO₂ and H₂Sthat have to be removed or reduced to less than 1% for CO₂ and 4 ppm forH₂S to meet the specifications for pipeline transportation.Particularly, wells in Saudi Arabia and Russia can contain up to 20%H₂S.

Biogas generally consists of methane (approx. 65% in volume), carbondioxide (approx. 35% in volume) and traces of hydrogen sulfide (<2%) andammonia (<1%). The high content of carbon dioxide and the presence ofhydrogen sulfide and ammonia make it unsuitable to be used in place ofnatural gas in gas distribution networks. Absence of hydrogen sulfide isa must to avoid corrosion in compressors, gas storage tanks, pipes andengines.

Current technologies for natural gas upgrading (e.g., removing one ormore of H₂S, CO₂, and condensable hydrocarbons) are often multi-stageprocesses, thus costly. In order to reduce costs and efficiency,industry desires selective adsorbents for the removal of CO₂, H₂S andcondensable hydrocarbons which exhibit high structure stability overmultiple sorption cycles.

SUMMARY

In general, embodiments of the present invention provide a method ofremoving compounds from a fluid. The method includes contacting one ormore metal organic framework (MOF) compositions with one or more fluids,such as natural gas and biogas, and sorbing one or more compounds, suchas of CO₂, H₂S and condensable hydrocarbons. In some embodiments, theone or more of CO₂, H₂S and/or condensable hydrocarbons can be sorbedsimultaneously or in series.

In some embodiments, the MOF is an M-soc-MOF, wherein M is a trivalentmetal. The trivalent metal can comprise gallium, indium, iron, scandium,or aluminum, in some embodiments. The M-soc-MOF can comprise a pluralityof 6-connected timer molecular building blocks (TMBBs) networked bytetradentate organic ligands, wherein each of the TMBBs can comprisethree metal carboxylate octahedra.

In some embodiments, the tetradentate organic ligands are rectangularplanar. In some embodiments, the tetradentate organic ligands comprisetetracarboxylate ligands. In some embodiments, the tetradentate organicligands comprise amidetetracarboxylate or3,3′,5,5′-azobenzenetetracarboxylate.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block flow diagram of a method of removing one ormore compounds from a fluid, according to an embodiment.

FIG. 2A illustrates a ball-and-stick structure and a polyhedralrepresentation of a trimer molecular building block, according to one ormore embodiments.

FIG. 2B illustrates a ball-and-stick structure and a polyhedralrepresentation of a suitable organic ligand, according to one or moreembodiments.

FIG. 2C illustrates a ball-and-stick structure and a polyhedralrepresentation of a M-soc-MOF, according to one or more embodiments.

FIG. 3 illustrates the results of a N₂ adsorption/desorption study for aM-soc-MOF, according to one or more embodiments.

FIG. 4A illustrates a H₂S/CO₂/N₂/CH₄:1/30/10/59 mixture adsorption datafor a Ga-soc-MOF, according to one or more embodiments.

FIG. 4B illustrates CO₂, H₂S, and CH₄ adsorption isotherms at 25° C. forthe Ga-soc-MOF, according to one or more embodiments.

DETAILED DESCRIPTION

Embodiments of the present invention provide the use of stable MOFs andMOF compositions, particularly M-soc-MOFs, for the subsequent (i.e., inseries) or simultaneous removal of CO₂, H₂S, and condensablehydrocarbons. Embodiments as described have the potential to reduce thenumber of processes in the natural gas or biogas overall treatmentscheme. It is expected that the regeneration of M-soc-MOF compositionswill be cost effective in comparison to conventional amine scrubbing.M-soc-MOF compositions also exhibit high affinity for condensablehydrocarbons (C₂H₆, C₃H₈, . . . ) at the inverse of zeolites andactivated carbons.

Metal organic frameworks (MOFs) are a versatile and promising class ofcrystalline solid state materials which allow porosity and functionalityto be tailored towards various applications. For example, MOF materialsexhibit exceptionally high specific surface area, in addition to tunablepore size and functionality (e.g., permeselectivity toward mono-branchedand n-paraffins), which make them suitable for many applicationsincluding gas storage, gas separation, catalysis, drug delivery,light-emitting devices, and sensing.

Generally, MOFs comprise a network of nodes and ligands, wherein a nodehas a connectivity capability at two or more functional sites, and aligand has a connectivity capability at least at two functional sites,each of which connect to a node. Nodes are typically metal ions or metalcontaining clusters. In some instances, ligands with node connectivitycapability at two or more functional sites can also be characterized asnodes. In some instances, ligands can include two functional sitescapable of each connecting to a node, and optionally one or moreadditional functional sites which do not connect to nodes within aparticular framework. In some embodiments, ligands can bepoly-functional, or polytopic, and comprise two or more functional sitescapable of each connecting to a node. In some embodiments, polytopicligands can be heteropolytopic, wherein at least one of the two or morefunctional sites differ from another functional site.

A MOF can comprise a metal-based node and an organic ligand whichextrapolate to form a coordination network. Such coordination networkshave advantageous crystalline and porous characteristics affectingstructural integrity and interaction with foreign species (e.g.,hydrocarbons). The particular combination of nodes and ligands within aframework will dictate the framework topology and functionality. Throughligand modification or functionalization, the environment in theinternal pores can be modified to suit specific applications.

MOF can be represented by the formula[(node)_(a)(ligand)_(b)(solvent)_(c)]_(n), wherein n represents thenumber of molecular building blocks. Solvent represents a guest moleculeoccupying pores within the MOF, for example as a result of MOFsynthesis, and can be evacuated after synthesis to provide a MOF withunoccupied pores. Accordingly, the value of c can vary down to zero,without changing the definitional framework of the MOF. Therefore, inmany instances, MOFs can be defined as [(node)_(a)(ligand)_(b)]_(n),without reference to a solvent or guest molecule component.

FIG. 1 illustrates a block flow diagram of a method 100 of removing oneor more compounds from one a fluid, according to an embodiment. Method100 includes contacting 102 one or more metal organic framework (MOF)compositions with a fluid and sorbing 104 one or more compounds from thefluid with the one or more MOF compositions. In particular, method 100includes contacting 102 one or more M-soc-MOF compositions with a fluidand sorbing 104 one or more compounds from the fluid with the one ormore M-soc-MOF compositions. Contacting 102 can include mixing, bringingin close proximity, chemically contacting, physically contacting orcombinations thereof. Fluids can include general liquids and gases. Insome embodiments, fluids include industrial process fluids. Examples ofspecific fluids include one or more of natural gas and biogas. Fluidscan further comprise water, including water in a liquid form, a gaseousform, or combinations thereof.

In one embodiment, sorbing 104 comprises absorbing. In one embodiment,sorbing 104 comprises adsorbing. In one embodiment, sorbing 104comprises a combination of adsorbing and absorbing. Sorbing 104 caninclude selective sorption (i.e., sorption of a single compound), orsimultaneous sorption (e.g., sorption of a plurality of compounds). TheM-soc-MOF compositions can sorb about 1% to about 99.9%, about 1% toabout 90%, about 1% to about 50% or about 1% to about 30% of one or morecompounds in a fluid. Sorbing 104 can occur at ambient temperature, atan elevated temperature, at a cooled temperature, or over a temperaturerange. In one embodiment, a temperature can be selectively changed tomanipulate sorption and/or desorption of different compounds. Sorbing104 can occur at ambient pressure, at an elevated pressure, at a cooledpressure, or over a pressure range. In one embodiment, pressure can beselectively changed to manipulate sorption and/or desorption ofdifferent compounds. In addition to or in the alternative to, aconcentration of one or more M-soc-MOF compositions can be varied toaffect a rate and/or magnitude of sorbing 104. One or more oftemperature, pressure and M-soc-MOF concentration can be regulated toproduce a simultaneous sorption of compounds, or a subsequent, step-wisesorption (i.e., in series) of compounds from a fluid. In series sorptiongenerally includes sorbing a quantity of a first compound via a MOF, andsubsequently sorbing a quantity of a second compound via the same MOFwhile at least a portion of the quantity of the first compound remainssorbed. Simultaneous sorption generally includes contacting a pluralityof compounds with an MOF, and sorbing a quantity of each of the twocompounds with the MOF.

One compound which can be sorbed by an M-soc-MOF from a fluid is CO₂.CO2 can be sorbed from a fluid comprising H₂O and/or CH₄ by an M-soc-MOFwith selectivity over one or more of H₂O and CH₄. One compound which canbe sorbed by an M-soc-MOF from a fluid is H₂S. H₂S can be sorbed from afluid comprising H₂O and/or CH₄ by an M-soc-MOF with selectivity overone or more of H₂O and CH₄. CO₂ and H₂S can be simultaneously sorbedfrom a fluid comprising H₂O and/or CH₄ by an M-soc-MOF with selectivityover one or more of H₂O and CH₄. CO₂ and H₂S can be sorbed from a fluidcomprising H₂O and/or CH₄ in series by an M-soc-MOF with selectivityover one or more of H₂O and CH₄. In a specific embodiment, CO₂ and H₂Scan be simultaneously sorbed from natural gas and/or biogas by anM-soc-MOF with selectivity over other one or more of H₂O and CH₄. In aspecific embodiment, CO₂ and H₂S can be sorbed from a fluid comprisingH₂O and/or CH₄ in series by an M-soc-MOF with selectivity over other oneor more of H₂O and CH₄. Generally, the above sorption abilities andstability in the presence of water of suitable M-soc-MOFs as disclosedherein is an advantageous aspect unavailable from other M-soc-MOFs andindustrial materials such as zeolites and activated carbon.

Condensable hydrocarbons can be sorbed by an M-soc-MOF from a fluid.Examples of condensable hydrocarbons include ethane, propane, butane,pentane, and hexane. In some embodiments, examples of condensablehydrocarbons include straight chained alkanes with 6 carbons or less.Condensable hydrocarbons and one or more of CO₂ and H₂S can besimultaneously sorbed from a fluid, with selectivity over other one ormore of H₂O and CH₄. Condensable hydrocarbons and one or more of CO₂ andH₂S can be sorbed in series from a fluid, with selectivity over otherone or more of H₂O and CH₄. The ability to sorb condensable hydrocarbonsis one advantageous aspect of suitable M-soc-MOFs as disclosed hereinover other materials such as zeolites and activated carbon.

M-soc-MOFs suitable for method 100 include M-soc-MOFs 200 comprising oneor more trimer molecular building blocks (TMBB) 201, as shown in FIG.2A, and one or more organic ligands 202, as shown in FIG. 2B. FIG. 2Aillustrates a ball-and-stick structure 201′ and a polyhedralrepresentation 201″ of a TMBB 201. FIG. 2B illustrates a ball-and-stickstructure 202′ and a polyhedral representation 202″ of one example of asuitable organic ligand 202. A TMBB 201 comprises three metalcarboxylate octahedra, each octahedral generally described as[MO₅(H₂O)], wherein M=a metal. A TMBB 201 can be generally described asM₃O_(x)(CO₂)_(y). One example of a TMBB 201 can be described as[Ga₃O(CO₂)₆(H₂O)₃]. One example of a TMBB 201 can be described as[In₃O(CO₂)₆]. One example of a TMBB 201 can be described as[Al₃O(CO₂)₆]. The three metal octahedra are metal-centered, and allshare one central μ₃-oxo anion. In each octahedron, the apical positioncan be occupied by a terminal water molecule. The metal-carboxylateclusters generate a rigid node with fixed geometry involving multiplemetal-oxygen coordination bonds which induce the stability of the nodeand subsequently enhance the thermal stability and overall rigidity ofthe framework.

Suitable metals (M) include trivalent metals (i.e., metals capable ofexhibiting a +3 oxidation state). Trivalent metals include aluminum,scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel,copper, gallium, germanium, arsenic, yittrium, zirconium, niobium,molybdenum, palladium, silver, indium, tin, antimony, lanthanum, cerium,praseodymium, samarium, europium gadolinium, terbium, erbium, thulium,ytterbium, lutetium, tantalum, tungsten, rhenium, osmium, iridium,platinum, gold, lead, and bismuth. Particularly suitable trivalentmetals include gallium, indium, iron, scandium, and aluminum. The threetrivalent metals yield an overall cationic framework (+1 per formulaunit) that is balanced by [NO₃]⁻¹ ions. The disordered [NO₃]⁻¹ ionsoccupy statistically two positions on the threefold axis with equalprobability. A broad range of suitable trivalent metals advantageouslyallows for M-soc-MOFs to be customized for particular purposes. Forexample, lighter trivalent metals can provide an M-soc-MOF withincreased sorption uptake per unit volume.

Each TMBB unit is linked by six separate organic ligands 202, as shownin FIG. 2A, to produce a novel 3D structure 200 having an soc-topology,as shown in FIG. 2C. Suitable ligands are tetradentate. Suitabletetradentate ligands include rectangular planar ligands. A generallysuitable ligand is a tetracarboxylate ligand. One particular suitableligand is amidetetracarboxylate:

One particular suitable ligand is 3,3′,5,5′-azobenzenetetracarboxylate:

FIG. 2C illustrates a ball-and-stick structure 200′ and a polyhedralrepresentation 200″ of a suitable M-soc-MOF 200 comprised of a pluralityof 6-connected TMBBs 201 networked by organic tetradentate planarligands 202. In FIG. 3C, hydrogen atoms, water molecules, and [NO₃]-ionsare omitted for clarity. One example M-soc-MOF 200 can be described as[In₃O(C₁₆N₂O₈H₆)_(1.5)(H₂O)₃](H₂O)₃(NO₃). All such M-soc-MOFs arecharacterized by an soc-topology, and can generally be denoted asM-soc-MOFs. The soc-topology of M-soc-MOF 200 provides unique structurefeatures, including the presence of isolated nanometer-scalecarcerand-like capsules, which anchor nitrate ions, and which arestrictly accessible through the two main channels by very restrictedwindows. Such characteristics provide high, localized charge densityadvantageous for chemical and physical sorption of compounds.

Other interesting structural features of the crystalline structure areits two types of infinite channels. The first type is hydrophilic, dueto the water molecules coordinated to the indium centers which arepointed inside these channels. Guest water molecules occupy theremaining free volume in these channels and form hydrogen bonds withcoordinated water molecules. The second type of channels can be guestfree, and have an approximately 1 nm diameter.

M-soc-MOFs can have a BET surface area of at least about 800 m²/g, atleast about 900 m²/g, at least about 1,000 m²/g, at least about 1,200m²/g, at least about 1,400 m²/g, or at least about 1,600 m²/g. In aspecific embodiment, an M-soc-MOF has a BET surface area of at leastabout 800 m²/g. In a specific embodiment, an M-soc-MOF has a BET surfacearea of about 1,000 m²/g. In a specific embodiment, an M-soc-MOF has aBET surface area of about 1,000 m²/g to about 1,600 m²/g.

M-soc-MOFs can have an average pore volume of at least about 0.2 cm³/g,at least about 0.25 cm³/g, at least about 0.3 cm³/g, at least about 0.45cm³/g, at least about 0.6 cm³/g, or at least about 0.65 cm³/g. In aspecific embodiment, an M-soc-MOF has an average pore volume of at leastabout 0.2 cm³/g. In a specific embodiment, an M-soc-MOF has an averagepore volume of about 0.3 cm³/g. In a specific embodiment, an M-soc-MOFhas an average pore volume of about 0.3 cm³/g to about 0.65 cm³/g.

EXAMPLE 1 Synthesis of Indium-soc-MOF

In this example, an In-soc-MOF formulated as[In₃O(C₁₆N₂O₈H₆)_(1.5)(H₂O)₃](H₂O)₃(NO₃) was synthesized by reacting3,3′,5,5′-azobenzenetetracarboxylic acid and In(NO₃)₃.2H₂O in aN,N-dimethylformamide (DMF)/CH₃CN solution in the presence ofpiperazine. The resulting In-soc-MOF consisted of orange polyhedralcrystals. It's structure included indium trimer building blocks, eachtrimer containing three {InO₅(H₂O)} octahedra sharing one central m3-oxoanions, and networked by six separate3,3′,5,5′-azobenzenetetracarboxylate ligands. The totalsolvent-accessible volume for the In-soc-MOF was determined to be 57.2%by summing voxels more than 1.2 Å away from the framework using PLATONsoftware. FIG. 3 illustrates the results of a N₂ adsorption/desorptionstudy, which revealed a reversible type I isotherm with no hysteresis.Such results are characteristic of a microporous material withhomogeneous pores. The estimated Langmuir surface area and pore volumefor In-soc-MOF are 1417 m2 g⁻¹ and 0.50 cm3 g⁻¹, respectively.

Other interesting structural features of the crystalline In-soc-MOFstructure are the two types of infinite channels. The first type ishydrophilic, because the water molecules coordinated to the indiumcenters are pointed inside these channels. Guest water molecules occupythe remaining free volume in these channels and form hydrogen bonds withcoordinated water molecules. The second type of channels have a diameterof approximately 1 nm diameter, and are guest-free as-synthesized.

The synthesis methods of this study are generally applicable to similarM-soc-MOFs, including those with lighter trivalent metals.

EXAMPLE 2 CO₂ and H₂ Sorption by Gallium-soc-MOF

This example utilizes use of metal organic frameworks as sorbents foruse in simultaneous or subsequent removal of CO₂ and H₂S. The Ga-soc-MOFin question is constructed based on the assembly of Gallium-carboxylatetrimer molecular building block (TMBB) and3,3′,5,5′-azobenzenetetracarboxylate. The oxygen-centeredgallium-carboxylate TMBB, [Ga₃O(CO₂)₆(H₂O)₃] comprises a 6-connectednode having trigonal-prismatic geometry networked by3,3′,5,5′-azobenzenetetracarboxylate tetradentate ligands.

FIG. 4A illustrates H₂S/CO₂/N₂/CH₄:1/30/10/59 mixture adsorptionexperiments performed in a column breakthrough set-up. The Ga-soc-MOFadsorbed H₂S and CO₂ from CH₄ with high selectivity. The 1% (of 15ml/min) H₂S was retained for 40 min, while 30% CO₂ (of 15 ml/min) wasretained for about 15 minutes, indicative of the potential of selectiveremoval of H₂S and CO₂ from CH₄ containing gas streams. FIG. 4Billustrates CO₂, H₂S, and CH₄ adsorption isotherms at 25° C. for theGa-soc-MOF, indicating selectivity for CO₂ and H₂S over CH₄.

What is claimed is:
 1. A metal organic framework (MOF) compositioncomprising: a M-soc-MOF composition having a square-octahedral topology(soc) and including one or more trimer molecular building blocks linkedto one or more organic ligands, wherein each trimer molecular buildingblock includes three metal (M) carboxylate octahedra.
 2. The MOFcomposition of claim 1, wherein at least one of the metal carboxylateoctahedra is characterized by the formula [MO₅(H₂O)], where M is ametal.
 3. The MOF composition of claim 1, wherein at least one of themetal carboxylate octahedra is characterized by the formulaM₃O_(x)(CO₂)_(y), where M is a metal, x is 1 or greater, and y is 0 orgreater.
 4. The MOF composition of claim 1, wherein the one or moretrimer molecular building blocks include a trivalent metal selected fromthe group consisting of aluminum, scandium, titanium, vanadium,chromium, manganese, iron, cobalt, nickel, copper, gallium, germanium,arsenic, yttrium, zirconium, niobium, molybdenum, palladium, silver,indium, tin, antimony, lanthanum, cerium, praseodymium, samarium,europium gadolinium, terbium, erbium, thulium, ytterbium, lutetium,tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, lead, andbismuth.
 5. The MOF composition of claim 1, wherein the one or moretrimer molecular building blocks include a trivalent metal selected fromthe group consisting of titanium, vanadium, chromium, manganese, cobalt,nickel, copper, germanium, arsenic, yttrium, zirconium, niobium,molybdenum, palladium, silver, tin, antimony, lanthanum, cerium,praseodymium, samarium, europium gadolinium, terbium, erbium, thulium,ytterbium, lutetium, tantalum, tungsten, rhenium, osmium, iridium,platinum, gold, lead, and bismuth.
 6. The MOF composition of claim 1,wherein the one or more organic ligands include tetradentate ligands. 7.The MOF composition of claim 6, wherein the tetradentate ligands includerectangular planar ligands.
 8. The MOF composition of claim 1, whereinthe one or more organic ligands include a tetracarboxylate ligand. 9.The MOF composition of claim 1, wherein the one or more organic ligandsinclude amidetetracarboxylate.
 10. The MOF composition of claim 1,wherein the one or more organic ligands include3,3′,5,5′-azobenzenetetracarboxylate.
 11. The MOF composition of claim1, wherein each trimer molecular building block is linked by sixseparate organic ligands.
 12. A method of removing one or more compoundsfrom a fluid, the method comprising: contacting a MOF composition ofclaim 1 with a fluid; and sorbing one or more compounds from the fluid.13. The method of claim 12, wherein the one or more compounds includeH₂S.
 14. The method of claim 12, wherein the one or more compoundsinclude CO₂.
 15. The method of claim 12, wherein the one or morecompounds include one or more condensable hydrocarbons.
 16. The methodof claim 15, wherein the one or more condensable hydrocarbons includeone or more of ethane, propane, butane, pentane, and hexane.
 17. Themethod of claim 12, wherein the one or more compounds are sorbedsimultaneously.
 18. The method of claim 12, wherein the one or morecompounds are sorbed in series.
 19. The method of claim 12, wherein thefluid includes natural gas.
 20. The method of claim 12, wherein thefluid includes biogas.